Identification of transcriptionally expressed pheromone receptor genes in filamentous ascomycetes

Detection of pheromone genes in filamentous ascomycetes implicated the presence of pheromone receptor genes. Similar to yeasts and basidiomycetes, these might be involved in a G-protein triggered signal transduction pathway during mating. We have identified two pheromone receptor genes, named pre1 and pre2, in the genome of the heterothallic filamentous ascomycete Neurospora crassa and the closely related homothallic Sordaria macrospora. The deduced pre1 gene product is a putative seven-transmembrane protein, which displays a high-level amino acid identity with the a-factor receptor Ste3p of Saccharomyces cerevisiae, and is also homologous to lipopeptide pheromone receptors of basidiomycetes. The deduced pre2 product displays significant sequence similarity with the S. cerevisiae STE2 gene product, the alpha-factor receptor. Pair-wise comparisons between pheromone receptor genes of N. crassa and S. macrospora revealed an extremely low degree of nucleotide conservation in these genes, suggesting that they evolved very rapidly. The two genes are transcriptionally expressed in both N. crassa and S. macrospora. Northern and reverse transcription-polymerase chain reaction analyses indicate that in N. crassa, expression of the receptor genes does not occur in a mating type specific manner. Thus, filamentous ascomycetes appear to posses and express pheromone receptor genes.